428 crank hole for pilot bearing

786 Views 38 Replies 11 Participants Last post by ponchonlefty, 11 d ago

Nate428

Discussion Starter · 23 d ago

Hi all. First post over here, seems my old go-to Pontiac forums are mostly gone, but this seems more well traveled.

I finally made time to get deep into a Tremec TKX 5 speed swap (Silver Sport kit) on my '79 Trans Am and I have hit a snag, hopefully not a brick wall. My car has a 1969 428 in it and I am replacing the TH400 that the prior owner had swapped in with the engine. Once I got the auto trans and flex plate out of the way I started to size things up to start bolting things on.

My problem is that the machined hole/pocket in the crank (see picture, second "step" into the hole) for the pilot bearing is, as near as I can measure about 1/16th of an inch too small for the pilot bearing SST sent me. I would assume that I should be able to wedge it in a little bit, but it is definitely not going in there, but as I said, it is really close.

I read somewhere that some Pontiac cranks were not machined to accept a pilot bearings if they were going into auto cars. I was hoping if that were the case for me that it would be more obvious, but it is pretty close, but definitely too small.

I sure don't want to yank the engine and buy a new bottom end if I'm just doing something wrong.

Does anyone here have any ideas what to look at/for? Thanks.

Azure Dishware Art Door Circle

See less See more

Reactions: 1

21 - 39 of 39 Posts

armyadarkness

· #21 · 21 d ago

I dont know if anyone mentioned it yet, but just use a bronze bushing and be done with it. They work fine and arent subject to the mechanical failures of needle bearings.

Reactions: 3

armyadarkness

· #22 · 21 d ago

lust4speed said:
Check bearing OD also. While I love Silver Sport to death they did send me the wrong bearing in my kit.

Since the bearing should measure 1.3780 as stated above, the crank hole should be slightly smaller in the range of 1.3778-1.3779 or so. If the fit is close but too tight I'd polish up the crank hole by hand with a Scotch Brite pad.

And FYI, Silver Sport is no longer the awesome company that everyone loves. They're now owned by a New Jersey attorney, and it shows in their ethics.

Reactions: 1

Nate428

Discussion Starter · #23 · 21 d ago

armyadarkness said:
I dont know if anyone mentioned it yet, but just use a bronze bushing and be done with it. They work fine and arent subject to the mechanical failures of needle bearings.

If i can get confirmation that a bushing will work for the Tremec box, I'll do that for sure. There seems to be an opinion that they require a bearing.

Bummer about SST. I bought my kit about a year ago, just now getting deeper into it.

Reactions: 2

armyadarkness

· #24 · 21 d ago

Yes a bushing will work... I had a similar issue and although I prefer bearings, I was more comfortable using the bushing. And for the record, I dont baby it.

Simply go to this thread and it lists the bushing that I used

www.gtoforum.com

FAQ - Powetrain: TREMEC TKX - Automatic to Manual Conversion

This is my final write up for the swap. It's NOT ANY CHEAPER to install a Muncie than a Tremec (if you're converting from an auto).. in fact, it's more expensive. A quality Muncie rebuild is going to cost over $2500, and then you have to buy a Hurst Competition Plus Shifter, linkage, doghouse...

www.gtoforum.com

www.gtoforum.com

Reactions: 2

armyadarkness

· #25 · 21 d ago

As for Silver Sport, customer service typically has no affect on their ability to sell parts, but... I just don't do business with companies who give poor service, and I also dont do business with Jersey attorneys... Now, they're both.

Reactions: 1

Nate428

Discussion Starter · #26 · 21 d ago

armyadarkness said:
Yes a bushing will work... I had a similar issue and although I prefer bearings, I was more comfortable using the bushing. And for the record, I dont baby it.

Simply go to this thread and it lists the bushing that I used

FAQ - Powetrain: TREMEC TKX - Automatic to Manual Conversion

This is my final write up for the swap. It's NOT ANY CHEAPER to install a Muncie than a Tremec (if you're converting from an auto).. in fact, it's more expensive. A quality Muncie rebuild is going to cost over $2500, and then you have to buy a Hurst Competition Plus Shifter, linkage, doghouse...

www.gtoforum.com

That's a relief, I did a bit more internet digging today and found someone chiming in from when SST was Kiesler saying that the bushings were a suitable alternative. The oil impregnated bronze seems like a good way to go there.

Thanks for the link.

Reactions: 2

armyadarkness

· #27 · 21 d ago

The world is filled with hardcore racers, using oil-lite bronze bushings. As I said, I do prefer bearings, but sometimes, despite my personal preferences, I let the application dictate the parts

Reactions: 2

Nate428

Discussion Starter · #28 · 21 d ago

Well, thankfully SST just called me back. They concurred that there's no problem with using a bronze bushing, so that's a relief. I'll be measuring the hole with divider calipers and telescoping gauge and talking with a local machinist to get it just right. Thanks for all of the input.

Reactions: 2

Nate428

Discussion Starter · #29 · 20 d ago

Divider calipers showed up yesterday, and I have a telescopic snap gauge coming too. The bore is almost dead on 34mm as close as I can tell without a micrometer. My Vernier calipers have a digital readout that goes to the hundredths, just need a new battery there. the bearing is stock sized 1.38 inches or 35mm. 1mm is 0.04 inches, so I'm about 40x what you could expect to press in. I'll measure about 100 more times before I get anything cut.

Reactions: 2

ponchonlefty

· #30 · 20 d ago

Nate428 said:
Divider calipers showed up yesterday, and I have a telescopic snap gauge coming too. The bore is almost dead on 34mm as close as I can tell without a micrometer. My Vernier calipers have a digital readout that goes to the hundredths, just need a new battery there. the bearing is stock sized 1.38 inches or 35mm. 1mm is 0.04 inches, so I'm about 40x what you could expect to press in. I'll measure about 100 more times before I get anything cut.

from your measurements it must not have been machined. but your right to check it more closely. i would think though calipers could get you closer than .040 . if you can get it straight in the hole. don't hurt to be cautious.so far it looks like the bronze bushing is the way to go.

Reactions: 1

PontiacJim

· #31 · 20 d ago

Nate428 said:
Well, thankfully SST just called me back. They concurred that there's no problem with using a bronze bushing, so that's a relief. I'll be measuring the hole with divider calipers and telescoping gauge and talking with a local machinist to get it just right. Thanks for all of the input.

You don't want to get a new crank, the stock one is a strong piece. So forget that idea.

I had the same experience with a previous 400 build. I used a bolt that fit through the brinze bushing hole, used a washer/nut to tighten it up, chucked it into my drill, and spun it on a fine flat file (must be at least the width of the bushing to get an even surface). Suppose you could also use sandpaper on a flat surface.

A little milling, and a little fitting. Took off "enough", but not to where it was loose. Did not use a caliper, but that would be the way to go in measuring the amount removed. Worked fine and no issues.

You will want to check the depth once the bushing is in. The input shaft on the trans has the alignment pin that goes into the bushing. Measure it for length and then the edged of the bushing to the inside machined hole in the crank. You should have enough depth that the trans input shaft end will not bottom out - or you will be jamming the input shaft into the crank and you won't like the results.

See less See more

Reactions: 2

Nate428

Discussion Starter · #32 · 20 d ago

PontiacJim said:
You don't want to get a new crank, the stock one is a strong piece. So forget that idea.

I had the same experience with a previous 400 build. I used a bolt that fit through the brinze bushing hole, used a washer/nut to tighten it up, chucked it into my drill, and spun it on a fine flat file (must be at least the width of the bushing to get an even surface). Suppose you could also use sandpaper on a flat surface.

A little milling, and a little fitting. Took off "enough", but not to where it was loose. Did not use a caliper, but that would be the way to go in measuring the amount removed. Worked fine and no issues.

You will want to check the depth once the bushing is in. The input shaft on the trans has the alignment pin that goes into the bushing. Measure it for length and then the edged of the bushing to the inside machined hole in the crank. You should have enough depth that the trans input shaft end will not bottom out - or you will be jamming the input shaft into the crank and you won't like the results.

I don't know if I trust myself with the drill lathe approach, but I did order 3 bronze bushings and could always get more for cheap now that I know the part number.

Good tip on watching how deep everything goes; I don't think the install instructions contemplate any depth issues, but with the bellhousing mocked up, that will be an easy measurement to take

Reactions: 3

armyadarkness

· #33 · 19 d ago

Nate428 said:
They concurred that there's no problem with using a bronze bushing, so that's a relief.

I love it when I know what Im talking about. It's like winning on a scratch off... rare, indeed.

Reactions: 3

PontiacJim

· #34 · 16 d ago

Nate428 said:
I don't know if I trust myself with the drill lathe approach, but I did order 3 bronze bushings and could always get more for cheap now that I know the part number.

Good tip on watching how deep everything goes; I don't think the install instructions contemplate any depth issues, but with the bellhousing mocked up, that will be an easy measurement to take

"Improperly aligned bell housing, transmission, or too long a pilot shaft can cause the main thrust bearing to fail. This alignment must be checked and corrected with offset dowel pins if necessary. If the pilot shaft “bottoms” in the crankshaft, the pilot shaft must be shortened. Thrust bearing failure is also caused by improperly shimmed or defective torque converters."

Reactions: 2

geeteeohguy

· #35 · 14 d ago

45 years ago I had an automatic trans 400 in my first GTO that had a crank not machined for the Pontiac bearing. I took measurements and had an oilight bronze bushing turned down for the proper press-fit. Not a problem. I prefer bearings where called for, but the bronze is more forgiving and will not fail like a bearing can. So another vote for a bronze bushing machined to fit your crank.

Reactions: 3

Montreux

· #36 · 11 d ago

Pay attention to what ponchonlefty said, and pay attention to the decimal point! Its a LIGHT press fit—0.0005 to 0.0010

If you’re using calipers, the smallest increment is 0.001”; you’ll have to eyeball the tenths (ten thousandths). Also, calipers will read slightly small when measuring ID’s because the width of the jaw causes it to bridge a little bit on the ID.

Reactions: 3

Montreux

· #37 · 11 d ago

If you go with a bushing...
Oilite is a brand name for an oil-impregnated sintered bronze material. If the shaft starts rubbing, the Oilite will “sweat” more oil right where its needed.
Typically it is sold in rough dimensional form and machined to fit. It is typically machined for a press fit into the hole. The press fit can cause the ID of the bushing to slightly collapse, which requires reaming the ID after installation.
Since you’re going to be dealing with a machine shop, and since you need fourth-digit accuracy (.0001), you may want to take the crank and the transmission to the machinist so he can make his own measurements.

Reactions: 3

Nate428

Discussion Starter · #38 · 11 d ago

I have down to hundredths of a mm, or .0004 inch on my caliper, but I don’t know if my technique with the dividers and snap gauge is that precise. Would love to have a machinist take the measurements, but the engine is still in the car. Still need to track one down and get his take.

Reactions: 1

ponchonlefty

· #39 · 11 d ago

Nate428 said:
I have down to hundredths of a mm, or .0004 inch on my caliper, but I don’t know if my technique with the dividers and snap gauge is that precise. Would love to have a machinist take the measurements, but the engine is still in the car. Still need to track one down and get his take.

i was a machinist. you want repeatability when measuring so the feel of resistance has to be the same when using snap gauges or dividers. it will take practice and patience to get it. practice on something and try to get the same dimensions its a delicate touch that is needed for accuracy. a micrometer is best but calipers can be used.

Reactions: 2

21 - 39 of 39 Posts